best left to a professional imo! you can't dye blonde over the top. blonde is what colour your hair is when colour is removed from your hair. you'll probably need it bleached or something to get back to blonde. Definately get a hairdresser to do that!
You can do it,but it's tricky. first you must choose the lightest blonding possible in one step. Then you will want to use a base ash blonde color on top of that. The ash will get rid of the rest of the red tones. Just use hot oil trestments and leave conditoner in your hair for long periods of time,so hair doesnt become too fried! And make sure you get a good trim when your done.
you would need to get your hair bleached, becuase if you just dye it blonde, you will probably end up with a n orange tone, since bleach drains all the color from your hair, you should just bleach it and it will remove your red and leave you with a vibrant blonde.